Polymers

ABSTRACT

The present invention is a polymer having structural units, units of formula I, units of formula II and units of either formula IIIa or formula IIIb: 
     
       
         
         
             
             
         
       
     
     The polymer improves the low-temperature properties of fuel oils from petroleum sources and especially from vegetable or animal sources.

This invention relates to polymers effective to improve thelow-temperature properties of fuel oils and to fuel oil compositionscontaining the polymers.

Fuel oils, whether derived from petroleum or from vegetable sources,contain components, e.g., n-alkanes or methyl n-alkanoates, that at lowtemperature tend to precipitate as large, plate-like crystals orspherulites of wax in such a way as to form a gel structure which causesthe fuel to lose its ability to flow. The lowest temperature at whichthe fuel will still flow is known as the pour point.

As the temperature of a fuel falls and approaches the pour point,difficulties arise in transporting the fuel through lines and pumps.Further, the wax crystals that form tend to plug fuel lines, screens,and filters at temperatures above the pour point. These problems arewell recognised in the art, and various additives have been proposed,many of which are in commercial use, for depressing the pour point offuel oils. Similarly, other additives have been proposed and are incommercial use for reducing the size and changing the shape of the waxcrystals that do form. Smaller size crystals are desirable since theyare less likely to clog a filter. The wax from a diesel fuel, which isprimarily an alkane wax, and the methyl n-alkanoates invegetable-derived fuels crystallize as platelets. Certain additivesinhibit this and cause the waxes to adopt an acicular habit, theresulting needles being more likely to pass through a filter, or form aporous layer of crystals on the filter, than are platelets. Otheradditives may also have the effect of retaining the wax crystals insuspension in the fuel, reducing settling and thus also assisting in theprevention of blockages.

The present invention is based on the discovery of certain types ofterpolymers and higher polymers which are effective to improve the lowtemperature properties of fuel oils. The polymers may find use in anytype of fuel but are particularly effective when used in fuel oils whichare derived from vegetable or animal sources such as fuel oilscomprising fatty acid alkyl esters and blends of these oils withpetroleum-derived fuel oils. These oils are often known as biodiesels orbiofuels and are commonly fatty acid methyl esters (FAME).

In accordance with a first aspect, the present invention provides apolymer comprising structural units of formula I, structural units offormula II and structural units of either formula IIIa or formula IIIb:

wherein R¹ and R² are the same or different and each represent a C₈ toC₂₂ alkyl group, preferably a C₁₂ to C₁₆ alkyl group; wherein R³represents —OCOR⁶, —COOR¹⁵, COOH, or a C₁ to C₂₂ alkyl group, preferablya C₁ to C₁₂ alkyl group, and R⁶ represents a C₁ to C₂₂ alkyl group,preferably a C₁ to C₁₂ alkyl group; wherein R⁴ is hydrogen, —COOH or—CH₂COOR¹⁶; wherein R¹⁵ and R¹⁶ are the same or different and eachrepresent a C₈ to C₂₂ alkyl group, preferably a C₁₂ to C₁₆ alkyl group;wherein R⁵ is hydrogen or methyl; wherein X represents a group offormula IV, formula V or formula VI:

wherein R⁷ represents hydrogen or a C₁ to C₈ alkyl group, R⁸ representsa C₁ to C₈ alkyl group, m is an integer from 1 to 10, and n is aninteger from 1 to 30, preferably from 5 to 20; wherein R⁹ is a C₁ to C₈alkyl linkage, R¹⁰, R¹¹ and R¹² are the same or different and eachrepresent hydrogen or a C₁ to C₈ alkyl group, p is an integer from 1 to10, and q is zero or an integer from 1 to 10; and wherein Y represents agroup of formula IV wherein R⁷ represents hydrogen or a C₁ to C₈ alkylgroup, R⁸ represents a C₁ to C₈ alkyl group, m is an integer from 1 to10, and n is an integer from 1 to 30, preferably from 5 to 20;and optionally, structural units of formula VII:

wherein R¹³ represents a C₈ to C₂₂ alkyl group, preferably a C₁₂ to C₁₆alkyl group; and wherein R¹⁴ is hydrogen or methyl.

Alkyl groups R¹ and R² may be linear or branched but are preferablylinear. Preferably R¹ and R² are the same and each represent a linearC₁₂ to C₁₄ alkyl group. In a preferred embodiment, R¹ and R² are each alinear C₁₂ alkyl group.

Preferably R³ represents —OCOR⁶.

Alkyl group R⁶ may be linear or if C₃ or larger, branched. Preferably R⁶represents a C₁-C₈ alkyl group. In a preferred embodiment R⁶ is methyl.

When present, alkyl groups R¹⁵ and R¹⁶ may be linear or branched but arepreferably linear. Preferably when present R¹⁵ and R¹⁶ are the same andeach represent a linear C₁₂ to C₁₄ alkyl group. In a preferredembodiment, when R¹⁵ and R¹⁶ are present they are each a linear C₁₂alkyl group.

Preferably R⁴ is hydrogen.

In a preferred embodiment, R³ represents —OCOR⁶ where R⁶ is methyl, andR⁴ is hydrogen. In another embodiment, R³ represents —OCOR⁶ where R⁶ is2-ethylhexyl, and R⁴ is hydrogen.

In a preferred embodiment, X represents a group of formula IV.Preferably R⁷ is hydrogen, R⁸ is methyl, m is an integer from 1 to 6,for example 1, 2 or 3 and n is an integer from 6 to 18, for example 9,10, 11, 12, 13, 14, 15 or 16.

In another preferred embodiment, X represents a group of formula V.Preferably R⁹ is a C₂ alkyl linkage, R¹⁰ and R¹¹ are both methyl, and qis zero.

Preferably Y represents a group of formula IV where R⁷ is hydrogen, R⁸is methyl, m is an integer from 1 to 6, for example 1, 2 or 3 and n isan integer from 6 to 18, for example 9, 10, 11, 12, 13, 14, 15 or 16.

When structural units of formula VII are present, alkyl group R¹³ may belinear or branched but is preferably linear. Preferably R¹³ represents alinear C₁₂ to C₁₆ alkyl group, for example a linear C₁₂ alkyl group or alinear C₁₄ alkyl group.

The polymer may contain further structural units but preferably thepolymer contains only structural units of formulae I, II, IIIa and/orIIIb or the polymer contains only structural units of formulae I, II,IIIa and/or IIIb and VII.

In a preferred embodiment the polymer comprises structural units offormulae I, II and IIIa wherein X represents a group of formula IV.

In a more preferred embodiment the polymer consists of structural unitsof formulae I, II and IIIa wherein X represents a group of formula IV.

In another preferred embodiment the polymer comprises structural unitsof formulae I, II and IIIb.

In a more preferred embodiment the polymer consists of structural unitsof formulae I, II and IIIb.

In another preferred embodiment the polymer comprises structural unitsof formulae I, II and IIIa wherein X represents a group of formula V.

In a more preferred embodiment the polymer consists of structural unitsof formulae I, II and IIIa wherein X represents a group of formula V.

In another preferred embodiment the polymer comprises structural unitsof formulae I, II, IIIb and VII.

In a more preferred embodiment the polymer consists of structural unitsof formulae I, II, IIIb and VII.

The proportion of each of the structural units present in the polymermay vary. Preferably units of formula I will comprise from 5 to 80% ofthe polymer on a molar basis, more preferably from 20 to 60%.

Preferably units of formula II will comprises from 5 to 70% of thepolymer on a molar basis, more preferably from 10 to 50%.

Preferably units of formula IIIa when present will comprise from 5 to60% of the polymer on a molar basis, more preferably from 10 to 50%.

Preferably units of formula IIIb when present will comprise from 5 to70% of the polymer on a molar basis, more preferably from 10 to 60%.

Preferably units of formula VII when present will comprise from 10 to50% of the polymer on a molar basis, more preferably from 15 to 40%.

The polymers preferably have a number average molecular weight (Mn)measured by GPC relative to polystyrene calibration standards of between500 and 50,000, more preferably between 500 and 35,000, most preferablybetween 1,000 and 20,000; for example between 5,000 and 15,000.

The polymers may be prepared by known methods. A suitable method is asolution phase polymerisation using suitable monomers and a free radicalinitiator. Any suitable solvent may be employed in the polymerisation.Cyclohexane, methyl ethyl ketone (MEK), toluene and ethyl alcohol haveall been found to be effective. Tert-butyl perpivalate has been found tobe a suitable free radical initiator although alternatives will be knownto those skilled in the art.

Non-limiting examples of suitable monomers to provide the polymer withstructural units of formula I include di-alkyl fumarates such asdi-dodecyl fumarate and di-tetradecyl fumarate. Non-limiting examples ofsuitable monomers to provide the polymer with structural units offormula II include vinyl esters such as vinyl acetate, vinyl2-ethylhexanoate and vinyl neodecanoate; alkyl and di-alkyl itaconates;maleic acid; and 1-alkenes. Non-limiting examples of suitable monomersto provide the polymer with structural units of formula IIIa includepoly(alkyleneglycol alkyl ether) acrylates or methacrylates such aspoly(ethyleneglycol methyl ether) acrylates and poly(ethyleneglycolmethyl ether) methacrylates; dialkylaminoalkyl acrylates ormethacrylates such as dimethylaminoethyl acrylate and dimethylaminoethylmethacrylate. Non-limiting examples of suitable monomers to provide thepolymer with structural units of formula IIIb includedi-poly(alkyleneglycol alkyl ether) fumarates such asdi-poly(ethyleneglycol methyl ether) fumarate. Non-limiting examples ofsuitable monomers to provide the polymer with structural units offormula VII include alkyl acrylates and alkyl methacrylates such asdodecyl acrylate and tetradecyl methacrylate.

In accordance with a second aspect, the present invention provides afuel oil composition comprising a major amount of a fuel oil and a minoramount of a polymer according to the first aspect.

In accordance with a third aspect, the present invention provides theuse of a polymer according to the first aspect to improve thelow-temperature proper ties of a fuel oil.

The Fuel Oil

The fuel oil may be, e.g., a petroleum-based fuel oil, especially amiddle distillate fuel oil. Such distillate fuel oils generally boilwithin the range of from 110° C. to 500° C., e.g. 150° C. to 400° C.

The invention is applicable to middle distillate fuel oils of all types,including the broad-boiling distillates, i.e., those having a 90%-20%boiling temperature difference, as measured in accordance with ASTMD-86, of 50° C. or more.

The fuel oil may comprise atmospheric distillate or vacuum distillate,cracked gas oil, or a blend in any proportion of straight run andthermally and/or catalytically cracked distillates. The most commonpetroleum distillate fuels are kerosene, jet fuels, diesel fuels,heating oils and heavy fuel oils. The heating oil may be a straightatmospheric distillate, or may also contain vacuum gas oil or crackedgas oil or both. The fuels may also contain major or minor amounts ofcomponents derived from the Fischer-Tropsch process. Fischer-Tropschfuels, also known as FT fuels, include those that are described asgas-to-liquid fuels, coal and/or biomass conversion fuels. To make suchfuels, syngas (CO+H₂) is first generated and then converted to normalparaffins and olefins by a Fischer-Tropsch process. The normal paraffinsmay then be modified by processes such as catalytic cracking/reformingor isomerisation, hydrocracking and hydroisomerisation to yield avariety of hydrocarbons such as isoparaffins, cyclo-paraffins andaromatic compounds. The resulting FT fuel can be used as such or incombination with other fuel components and fuel types such as thosementioned in this specification.

The invention is particularly applicable to fuel oils containing fattyacid alkyl esters made from oils derived from animal or vegetablematerials, often called biofuels or biodiesels. Biofuels are believed tobe less damaging to the environment on combustion and are obtained froma renewable source. It has been reported that on combustion less carbondioxide is formed by the equivalent quantity of petroleum distillatefuel, e.g. diesel fuel, and very little sulphur dioxide is formed.

Examples of oils derived from animal or vegetable material are rapeseedoil, coriander oil, soyabean oil, cottonseed oil, sunflower oil, castoroil, olive oil, peanut oil, maize oil, almond oil, palm kernel oil,coconut oil, mustard seed oil, jatropha oil, beef tallow and fish oils.Further examples include oils derived from corn, jute, sesame, shea nut,ground nut and linseed oil and may be derived therefrom by methods knownin the art. Rapeseed oil, which is a mixture of fatty acids partiallyesterified with glycerol is available in large quantities and can beobtained in a simple way by pressing from rapeseed. Recycled oils suchas used kitchen oils are also suitable.

As alkyl esters of fatty acids, consideration may be given to thefollowing, for example as commercial mixtures: the ethyl, propyl, butyland especially methyl esters of fatty acids with 12 to 22 carbon atoms,for example of lauric acid, myristic acid, palmitic acid, palmitoleicacid, stearic acid, oleic acid, elaidic acid, petroselic acid,ricinoleic acid, elaeostearic acid, linoleic acid, linolenic acid,eicosanoic acid, gadoleic acid, docosanoic acid or erucic acid, whichhave an iodine number from 50 to 150, especially 90 to 125. Mixtureswith particularly advantageous properties are those which containmainly, i.e. to at least 50 wt % methyl esters of fatty acids with 16 to22 carbon atoms and 1, 2 or 3 double bonds. The preferred alkyl estersof fatty acids are the methyl esters of oleic acid, linoleic acid,linolenic acid and erucic acid.

Commercial mixtures of the stated kind are obtained for example bycleavage and esterification of animal and vegetable fats and oils bytheir transesterification with lower (ca. C₁ to C₆) aliphatic alcohols.For production of alkyl esters of fatty acids it is advantageous tostart from fats and oils which contain low levels of saturated acids,less than 20%, and which have an iodine number of less than 130. Blendsof the following esters or oils are suitable, e.g. rapeseed, sunflower,coriander, castor, soyabean, peanut, cotton seed, beef tallow etc. Alkylesters of fatty acids based on certain varieties of rapeseed oil havingmore than 80 wt % of unsaturated fatty acids with 18 carbon atoms, areparticularly suitable.

Whilst all of the above oils may be used as biofuels, preferred arevegetable oil derivatives, of which particularly preferred biofuels arealkyl ester derivatives of rapeseed oil, cottonseed oil, soyabean oil,sunflower oil, olive oil, or palm oil, rapeseed oil methyl ester beingespecially preferred.

The invention is applicable to pure biofuels. In one embodimenttherefore, the fuel oil comprises essentially 100% by weight of an oilderived from a plant or animal source, preferably essentially 100% byweight of fatty acid alkyl esters, most preferably fatty acid methylesters.

Biofuels are commonly used in combination with petroleum-derived oils.The present invention is also applicable to mixtures of biofuel andpetroleum-derived fuels in any ratio. Such fuels are often termed Bxfuels where x represents the percentage by weight of biofuel in thebiofuel-petroleum blend. Examples, include fuels where x is 2 or above,preferably 5 or above, for example up to 10, 25, 50, or 95. Preferablythe biofuel component in such Bx fuels comprises fatty acid alkylesters, most preferably fatty acid methyl esters.

The fuel oil, whether petroleum or vegetable or animal-derivedpreferably has a low sulphur content. Typically, the sulphur content ofthe fuel oil will be less than 500 ppm (parts per million by weight).Preferably, the sulphur content of the fuel oil will be less than 100ppm, for example, less than 50 ppm. Fuel oils with even lower sulphurcontents, for example less that 20 ppm or less than 10 ppm are alsosuitable.

The amount of polymer present in the fuel oil may vary according to thetype of fuel oil and the low-temperature properties required from thefuel oil. Suitably the polymer will be present in the fuel oil in anamount of between 10 and 5,000, preferably between 10 and 1,000, morepreferably between 50 and 500 ppm by weight based on the weight of thefuel oil.

As in known in the art, fuel additives are commonly supplied in the formof an additive concentrate comprising one or more fuel additives in asuitable carrier fluid or solvent. In accordance with a fourth aspect,the present invention provides an additive concentrate comprising apolymer according to the first aspect and a compatible solvent orcarrier therefor. Examples of suitable solvents and carrier fluids areknown in the art and include hydrocarbon solvents such as naphtha,kerosene, diesel and heater oil, aromatic hydrocarbons such as thosesold under the ‘SOLVESSO’ trade name, alcohols, ethers and otheroxygenates and paraffinic hydrocarbons such as hexane, pentane andisoparaffins. The carrier fluid or solvent is chosen having regard toits compatibility with both the polymer and the fuel oil.

The polymers of the present invention may be provided to the fuel oildirectly or in the form of an additive concentrate.

The polymers of the present invention may also find use in lubricatingoils as flow-improvers or pour point depressants.

Further Additives

Other additives capable of altering the low-temperature properties offuel oil may be combined with the polymers of the present invention.Suitable materials will be known to those skilled in the art and includeflow-improvers such as ethylene-unsaturated ester copolymers andterpolymers, for example, ethylene-vinyl acetate copolymers,ethylene-vinyl 2-ethyl hexanoate copolymers and ethylene-vinylneodecanoate copolymers, ethylene-vinyl acetate-vinyl 2-ethyl hexanoateterpolymers, ethylene-vinyl acetate-vinyl neononanoate terpolymers,ethylene-vinyl acetate-vinyl neodecanoate terpolymers; comb polymerssuch as fumarate-vinyl acetate copolymers; hydrocarbon polymers such ashydrogenated polybutadiene copolymers, ethylene/1-alkene copolymers, andsimilar polymers. Also suitable are additives known in the art as waxanti-settling additives (WASA). Also suitable are condensate speciessuch as alkyl-phenol formaldehyde condensates as described in EP 0 857776 B1, or hydroxy-benzoate formaldehyde condensates as described inEP-A-1 482 024.

The present invention contemplates the addition of such additionaladditives; their application in terms of treat rate being known to thoseskilled in the art. In a preferred embodiment the polymers of theinvention are combined with, or used in combination with, one or more ofan ethylene-unsaturated ester copolymer, a wax anti-settling additive,an alkyl-phenol formaldehyde condensate or a hydroxy-benzoateformaldehyde condensate. In a more preferred embodiment the polymers ofthe invention are combined with, or used in combination with, anethylene-unsaturated ester copolymer, a wax anti-settling additive, andone or both of an alkyl-phenol formaldehyde condensate or ahydroxy-benzoate formaldehyde condensate. Particularly preferredethylene-unsaturated ester copolymers are ethylene-vinyl acetatecopolymers ethylene-vinyl acetate vinyl 2-ethyl hexanoate terpolymers,ethylene-vinyl acetate vinyl neononanoate terpolymers and ethylene-vinylacetate vinyl neodecanoate terpolymers. A particularly preferred waxanti-settling additive is the amide-amine salt formed by the reaction ofphthalic anhydride with two molar proportions of di-hydrogenated tallowamine. Any additional additives may be introduced separately to the fueloil composition of the first aspect or combined with the polymers of theinvention into the additive concentrates of the fourth aspect.

The invention will now be described by way of example only.

Preparation of the Polymers

The following example illustrates the synthesis of a polymer as used inthe present invention. The same method was used to make all otherpolymers.

Di-dodecyl fumarate (15.40 g, 34.01 mmol), vinyl acetate (1.87 g, 21.72mmol) and poly(ethyleneglycol methyl ether) acrylate ester having anumber average molecular weight of 454 gmol⁻¹ (3.27 g, 7.20 mmol) wereplaced in a Schlenk tube together with cyclohexane (10 ml). The mixturewas degassed and then heated with stirring to 80° C. under a nitrogenatmosphere. Tert-butyl perpivalate (0.1 ml, 50:50 wt % in cyclohexane)was added to the mixture to initiate polymerisation. Additionalinitiator was added to the mixture every hour over the course of thenext four hours. Once five hours had elapsed, the mixture was allowed tocool and the product obtained.

Table 1 below details the polymers which were prepared using thefollowing monomers:

TABLE 1

Polymer monomer 1 monomer 2 monomer 3 monomer 4 solvent Mn 1 C₁₂F(34.07) VA (21.72) ^(†)PEGOMeA (7.20) — cyhex 13.973 2 C₁₂F (34.07) VA(21.72) ^(†)PEGOMeA (7.20) — MEK 14.306 3 C₁₂F (34.07) VA (21.72)^(†)PEGOMeA (7.20) — EtA 14.775 4 C₁₂F (34.07) VA (21.72) ^(†)PEGOMeA(7.20) — tol 12.575 5 C₁₂F (34.07) VA (14.66) ^(†)PEGOMeA (14.41) — MEK9.438 6 C₁₂F (34.07) VA (14.66) ^(†)PEGOMeA (14.41) — EtA 8.808 7 C₁₂F(34.07) VA (14.66) ^(†)PEGOMeA (14.41) — tol 8.168 8 C₁₂F (34.07) VA(21.72) ^(‡)PEGOMeA (7.86) — MEK 13.487 9 C₁₂F (34.07) VA (21.72)^(‡)PEGOMeA (7.86) — EtA 6.367 10 C₁₂F (34.07) VA (21.72) ^(‡)PEGOMeA(7.86) — tol 10.843 11 C₁₂F (34.07) VA (21.72) ^(†)PEGOMeA (7.20) — EtA5.798 12 C₁₂F (34.07) VA (21.72) ^(†)PEGOMeA (7.20) — tol 6.465 13 C₁₂F(34.09) VA (21.28) PEGOMeMA (7.09) — EtA 5.640 14 C₁₂F (34.09) VA(14.19) PEGOMeMA (14.21) — EtA 3.227 15 C₁₂F (34.09) VA (21.28) PEGOMeMA(7.09) — EtA 1.888 16 C₁₂F (34.09) VA (21.28) DMAEA (7.13) — EtA 1.36017 C₁₂F (34.09) VA (14.19) DMAEA (14.20) — EtA 1.098 18 C₁₂F (34.09) VA(7.09) DMAEA (21.33) — EtA 904 19 C₁₂F (25.60) VA (28.23) PEGOMeF (8.52)— EtA 3.284 20 C₁₂F (17.12) VA (28.57) PEGOMeF (17.08) — EtA 1.960 21C₁₂F (8.61) VA (28.57) PEGOMeF (25.60) — EtA 1.393 22 C₁₂F (25.69) VA(14.87) PEGOMeF (8.57) C₁₂A (14.04) EtA 4.221 23 C₁₂F (17.07) VA (13.82)PEGOMeF (20.13) C₁₂A (14.29) EtA 1.998 24 C₁₂F (8.59) VA (14.40) PEGOMeF(25.55) C₁₂A (14.17) EtA 1.723 25 C₁₂F (25.53) VA (14.30) PEGOMeF (8.53)C₁₄MA (14.08) EtA 6.860 26 C₁₂F (17.12) VA (14.18) PEGOMeF (17.08) C₁₄MA(14.26) EtA 4.491 27 C₁₂F (8.67) VA (14.41) PEGOMeF (25.57) C₁₄MA(14.33) EtA 1.545 Key: ^(†)PEGOMeA = PEGOMeA monomer of Mn 454;^(‡)PEGOMeA = PEGOMeA monomer of Mn 804; (—, —) = amount of each monomerused in mmol; cyhex = cyclohexane; MEK = methyl ethyl ketone; EtA =ethyl alcohol; tol = toluene

The polymers prepared were tested for their CFPP (Cold Filter PluggingPoint) performance. CFPP is a standard industry test to evaluate theability of a fuel oil sample to flow through a filter at reducedtemperature. The test which is carried out by the procedure described indetail in “Jn. Of the Institute of Petroleum”, vol. 52, No. 510 (1996),pp 173-285, is designed to correlate with the cold flow of a middledistillate in automotive diesels. In brief, a sample of the oil to betested (40 cm³) is cooled in a bath which is maintained at about −34° C.to give linear cooling at about 1° C./min. Periodically (at each onedegree centigrade starting from above the cloud point), the oil istested for its ability to flow through a fine screen in a prescribedtime period using a test device which is a pipette to whose lower end isattached an inverted funnel which is positioned below the surface of theoil to be tested. Stretched across the mouth of the funnel is a 350 meshscreen having an area defined by a 12 mm diameter. The periodic testsare initiated by applying a vacuum to the upper end of the pipettewhereby oil is drawn through the screen up into the pipette to a markindicating 20 cm³ of oil. After each successful passage, the oil isreturned immediately to the CFPP tube. The test is repeated with eachone degree drop in temperature until the oil fails to fill the pipettewithin 60 seconds, the temperature at which failure occurs beingreported as the CFPP temperature.

Table 2 below show the CFPP performance of the polymers in a biodieselfuel oil which was a 75:25 by weight mixture of rape-seed methyl ester(RME) and soya-oil methyl ester (SME). The CFPP of the untreated fuelwas −11.0° C. The polymers were tested in an additive formulation whichalso contained an ethylene-vinyl acetate copolymer, a wax anti-settlingadditive being the amide-amine salt formed by the reaction of phthalicanhydride with two molar proportions of di-hydrogenated tallow amine anda hydroxy-benzoate formaldehyde condensate. Each column gives theaverage measured CFPP value for the indicated treat-rate of polymer ofthe invention which is given in parts per million by weight based on theweight of the fuel oil. Where no value appears this indicates that nomeasurement was taken.

TABLE 2 Polymer 82 wppm 165 wppm 247 wppm 330 wppm 412 wppm 1 −13.8−17.3 −23.0 — −21.0 2 −13.0 −18.0 −19.5 −16.3 — 3 −12.5 −17.5 −19.5−19.5 — 4 −13.0 −19.0 −19.0 −17.5 — 5 −12.3 −17.8 −19.8 −21.3 −19.0 6−14.5 −19.0 −22.5 −23.5 — 7 −13.5 −18.5 −22.0 −21.8 −17.3 8 −12.5 −18.0−20.0 −20.5 — 9 −13.0 −17.8 −20.5 −21.0 −20.5 10  −12.8 −17.0 −19.8−21.3 −21.5 11  −14.0 −17.5 −20.5 −20.5 — 12  −14.5 −19.0 −21.5 −20.0 —Polymer 74 wppm 147 wppm 221 wppm 295 wppm 13 −14.0 −19.0 −19.0 −19.8 14−15.0 −19.0 −22.0 −20.5 15 −15.5 −19.0 −20.0 −20.0 19 −14.3 −19.0 −20.0−20.0 20 −11.5 −19.0 −19.0 −13.0 21 −12.0 −18.0 −11.0 −12.0 22 −13.0−18.0 −19.5 −18.3 23 −13.5 −15.5 −21.5 −18.0 24 −15.0 −18.5 −17.5 −14.025 −14.0 −18.0 −17.5 −19.5 26 −14.0 −18.0 −21.0 −18.5 27 −12.0 −17.5−18.0 −18.8

1. A polymer comprising structural units of formula I, structural unitsof formula II and structural units of formula IIIb:

wherein R¹ and R² are the same or different and each represent a C₈ toC₂₂ alkyl group, preferably a C₁₂ to C₁₆ alkyl group; wherein R³represents —OCOR⁶, —COOR¹⁵, —COOH, or a C₁ to C₂₂ alkyl group,preferably a C₁ to C₁₂ alkyl group, and R⁶ represents a C₁ to C₂₂ alkylgroup, preferably a C₁ to C₁₂ alkyl group; wherein R⁴ is hydrogen, —COOHor —CH₂COOR¹⁶; wherein R¹⁵ and R¹⁶ are the same or different and eachrepresent a C₈ to C₂₂ alkyl group, preferably a C₁₂ to C₁₆ alkyl group;wherein Y represents a group of formula IV:

wherein R⁷ represents hydrogen or a C₁ to C₈ alkyl group, R⁸ representsa C₁ to C₈ alkyl group, m is an integer from 1 to 10, and n is aninteger from 1 to 30, preferably from 5 to
 20. 2-8. (canceled)
 9. Thepolymer according to claim 1, wherein Y represents a group of formula IVwhere R⁷ is hydrogen, R⁸ is methyl, m is an integer from 1 to 6 and n isan integer from 6 to
 18. 10-11. (canceled)
 12. A fuel oil compositioncomprising a major amount of a fuel oil and a minor amount of thepolymer recited in claim
 1. 13. The fuel oil composition according toclaim 12, wherein the fuel oil contains fatty acid alkyl esters madefrom oils derived from animal or vegetable materials.
 14. An additiveconcentrate comprising the polymer recited in claim 1 and a solvent. 15.A polymer according to claim 1 wherein R¹ and R² are the same and eachrepresent a linear C₁₂ to C₁₄ alkyl group.
 16. A polymer according toclaim 1 wherein R³ represents —OCOR⁶.
 17. A polymer according to claim16 wherein R⁶ is methyl or 2-ethylhexyl and R⁴ is hydrogen.
 18. Apolymer according to claim 1 further comprising structural units offormula VII,

wherein R¹³ represents a C₈ to C₂₂ alkyl group, preferably a C₁₂ to C₁₆alkyl group; and wherein R¹⁴ is hydrogen or methyl.
 19. A polymeraccording to claim 18 wherein R¹³ represents a linear C₁₂ to C₁₆ alkylgroup.